1. Field of the Invention
The present invention relates to a method of cleaning metallic works such as machine parts heat treated by oil quenching or the like and also relates to a cleaning apparatus.
2. Description of the Related Art
Steels parts such as gears and shafts used for a vehicle driving mechanism are frequently oil quenched. The oil quenching is performed by immersing works heated at a predetermined temperature in quenching oil, and much quenching oil is attached to the surfaces of the works. In order to remove the quenching oil, the works are cleaned by using a liquid cleaner such as water or an alkaline cleaner. Jpn. Pat. Appln. Kokoku Publication No. 56-5826, for example, discloses a cleaning method using a liquid cleaner boiled by heat of works generated by immersing the heated works in the liquid cleaner. In this prior art, the temperature of the liquid cleaner is maintained at 98.degree. C. to 99.degree. C. which is close to its boiling point, and the works are heated to a temperature higher than the boiling point of the cleaner. Oil is removed from the surfaces of the works by bubbles produced from the boiling liquid cleaner. Since, however, cleaning is made only once, such a problem is likely to arisen that the quenching oil is not completely removed from the surfaces of the works. A further problem is likely to occur that the liquid cleaner is mixed with much quenching oil when the works are immersed in the liquid cleaner soon after the oil quenching process. As affinity between the oil and the liquid cleaner heated to a temperature close to its boiling point is high, much oil is emulsified in the liquid cleaner, and it becomes difficult to separate the oil from the liquid cleaner, making it hard to remove the oil from the liquid cleaner. In addition, the oil in the liquid cleaner is easily attached to the works again when the works are taken out of the liquid cleaner. When an alkaline cleaner as a liquid cleaner is heated to a temperature close to its boiling point as described in the above Publication, the continuity of oil removing ability of the cleaner is greatly reduced. Thus, the liquid cleaner must be exchanged or supplemented frequently, thereby increasing the running cost.